Effect Of Salinity On Cable Bacteria Species Composition And Diversity.

Cable bacteria are Desulfobulbaceae that couple sulphide oxidation to oxygen reduction over centimetre distances by mediating electric currents. Recently it was suggested that the cable bacteria clade is composed of two genera, Ca. Electronema and Ca. Electrothrix, with distinct freshwater and marine habitats, respectively. However, only a few studies have reported cable bacteria from freshwater sediment, making this distinction uncertain. Here we report novel data to show that salinity is a controlling factor for the diversity and the species composition within cable bacteria populations. Cable bacteria sampled from a freshwater site (salinity 0.3) grouped into Ca. Electronema and could not grow under brackish conditions (salinity 21), whereas cable bacteria from a brackish site (salinity 21) grouped into Ca. Electrothrix and decreased by 93% in activity under freshwater conditions. On a regional scale (Baltic Sea), salinity significantly influenced species richness and composition. However, other environmental factors, such as temperature and quantity and quality of organic matter were also important to explain the observed variation. A global survey of 16S rRNA gene amplicon sequencing revealed that the two genera did not co-occur likely because of competitive exclusion and identified a possible third genus. This article is protected by copyright. All rights reserved.